This disclosure relates generally to means for detecting the presence of Neisseria bacteria utilizing an immunoassay technique and is particularly directed to the use of (NH.sub.4).sub.2 SO.sub.4 to precipitate the antigen-antibody complex.
The importance of being able to quickly and accurately detect the presence of Neisseria bacteria, especially Neisseria gonorrhoeae, is well recognized. Conventional tests for determining the presence of organisms such as N. gonorrhoeae require the preparation of bacteria cultures or the use of serological methods. Such tests, however, have known limitations. See, for example, the publication "International Symposium on Gonorrhea", B. B. Diena, Ed., a collection of papers presented at the Oct., 1973 International Symposium on Gonorrhea sponsored by the Health Protection Branch, Health and Welfare Canada, Ottawa, especially at p. 34 et seq.
In the related application cited above entitled "Detecting Neisseria Bacteria" there is disclosed a relatively simple and quick test for determining the presence of Neisseria in liquid samples. That test resulted from the discovery of an enzyme in Neisseria bacteria which appears to be specific to those organisms. The enzyme demonstrates the capability for oxidizing 1,2-propanediol and reducing nicotinamide-adenine-dinucleotide (NAD). Therefore, whereas the full compositional and structural parameters of the enzyme are not understood and no identification has been found in the literature, the oxidizing-reducing behavior exhibited by the enzyme has led to the application of the name 1,2-propanediol dehydrogenase thereto, and that application will be utilized throughout this specification.
It is well known that a specific biochemical reaction frequently takes place between an antibody and its homologous antigen thereby creating an antibody-antigen complex. Where an enzyme is the antigen, the reaction thereof with its specific antibody results in the activity of the enzyme being significantly inhibited. An excellent discussion of this phenomenon can be found in "Immunochemistry of Enzymes and Their Antibodies", M. J. Salton, John Wiley & Sons, New York (1977). Utilizing this reaction, then, one can detect the presence of a particular enzyme by bringing the antibody specific thereto into contact with the said enzyme and testing the result of the reaction therebetween for a decrease in enzyme activity.
The use of that practice for the determination of the presence of Neisseria bacteria in a liquid sample is described in the above-cited related application entitled "Detection of Neisseria Bacteria by Immunoassay". Hence, that invention is based upon using antibodies specific to the enzyme present in Neisseria bacteria, i.e., the 1,2-propanediol dehydrogenase described above, to inhibit the activity of the enzyme in an assay sample. In so doing, antibody specificity is inferred on the assay of the enzyme. Therefore, the procedure combines the sensitivity of an enzymatic reaction with the specificity of an immunoassay.
The instant invention comprises a modification of the method described in the latter patent application wherein (NH.sub.4).sub.2 SO.sub.4 precipitation of the antigen-antibody complex acts to concentrate the enzyme, remove interfering materials, and, thereby, improve the speed and precision of the assay. The method is particularly useful with N. gonorrhoeae.